1. Field of the Invention
The invention relates to a process for the preparation of high purity basic zirconium carbonate. The basic zirconium carbonate generally corresponds to the formula EQU Zr.sub.2 O.sub.3 (OH).sub.2.CO.sub.2.7H.sub.2 O
2. Description of the Prior Art
Basic zirconium carbonate is used in the form of an aqueous paste in the textile industry in finishing processes. It is additionally an important intermediate for the preparation of other zirconium salts which are prepared from the basic zirconium carbonate, for example, by the action of acid. Basic zirconium carbonate may in addition be converted into zirconium oxide by calcining which has attained importance, especially in the ceramics industry. In many cases, a zirconium compound of high purity is required. The purity requirements for zirconium oxide which is intended to be used in electroceramics are particularly high.
Because basic zirconium carbonate is partially used as is and partially as an intermediate, there is considerable interest in preparing this product in high purity.
It is possible to produce very pure zirconium tetrachloride by repeated sublimation in an atmosphere of hydrogen and to convert this by known procedures into the oxide. This process, however, is too expensive for practical purposes.
The preparation of solutions of very pure zirconium oxychloride by the repated recrystallization of the oxychlorides is known. This procedure is also very complicated and consequently, too expensive for industrial application.
German Offenlegungsschrift No. 28 54 200 discloses a process for the preparation of zirconium oxide in which technical calcium zirconate is the starting material. After being dissolved in hydrochloric acid, the basic zirconium sulfate is precipitated and then, reprecipitated as the basic zirconium carbonate. Finally, the material is calcined. In the practical application of this process, however, difficulties arise in the precipitation of the basic zirconium sulfate. Particularly, one either obtains a product of high purity, but low yield, or a slightly contaminated product, which is precipitated almost quantitatively, depending on the fluoride content.